Spectral assessment of fruit

ABSTRACT

Apparatus for the spectral assessment of fruit comprising a sensor head ( 10 ) positioned adjacent a near infrared light source ( 11 ), the sensor head being coupled to a spectrometer via fibre optics ( 30 ), the sensor head being positioned close to the periphery of fruit substantially parallel with the light from the light source so that the fibre optics sense only the internally reflected or refracted light emanating from the fruit.

INTRODUCTION

[0001] This invention relates to spectral assessment of fruit and inparticular relates to an optical configuration that can be used tospectrally assess characteristics of fruit. The invention also embracesan assembly that can spectrally assess fruit as it is transported on aconveyor.

BACKGROUND OF THE INVENTION

[0002] The monitoring of eating quality of fruit and vegetables byobjective methods is usually destructive and slow (eg squeezing juice tomeasure Brix). There is a need to be able to rapidly and non-invasivelyevaluate the internal quality of fresh fruit and vegetables which mayenter the fresh market channels or be used for processing. Nearinfra-red spectroscopy (NIRS), nuclear magnetic resonance (NMR), andacoustic techniques all offer potential for the non-invasive assessmentof the internal composition of intact fruit. Of the above NIRS is themost advanced technique with regard to instrumentation, applications,accessories and chemometric software packages, and with respect to costand speed of operation.

[0003] Near infra-red light (NIR) is a small part of the spectrum ofelectromagnetic radiation—which starts at high-energy waves such asx-rays, through the visible spectrum, to low energy waves such asmicrowaves and radio waves. NIR is next to the visible portion of lightand is a natural part of sunlight. NIR is typically defined as radiationof wavelengths 700-2500 nm, which is invisible to the human eye.

[0004] Specific molecules can absorb specific wavelengths. Thischaracteristic is useful in the identification and quantification of agiven compound. Absorption of ultraviolet and visible light isassociated with the transition of electrons between orbitals in an atomor molecule. Absorption of infra-red radiation by biological materialprincipally involves the rotation and stretching of N—H, C—H and O—Hbonds. These bonds are associated with constituents of interest to fruitquality evaluation, including sugar, starch, protein, lipids and water.The infra-red absorption spectrum is commonly used by organic chemiststo fingerprint organic molecules. However, ultraviolet, visible andinfra-red radiation have poor penetration through bulk tissue. Inessence, techniques relying on these wavelengths are useful forsolutions or for surface studies. Fortunately, the near infra-red regionof the electromagnetic spectrum does penetrate relatively well throughbulk biological material, and this region also carries an echo, ofinformation of the infrared absorption spectrum. Unfortunately, thesecond and third overtone absorption bands which occur in the nearinfra-red region are weak and broad, and thus NIRS have been a ‘slowstarter’ relative to other techniques, and are only now achievingwidespread commercial application.

[0005] NIRS technology has been trialed in horticultural applicationsfor over 20 years. However, recent developments in fibre optics, arraydetectors computing power of PCs and of software capable of carrying outthe complex statistical mathematics has made application to inline fruitpacking possible.

[0006] Past proposals involve the use of either reflector spectroscopy,with a detector viewing an illuminated area of the fruit, or partialtransmittance spectroscopy with the detector mounted at an angle awayfrom detector. The detector is commonly an array spectrometer, allowingspectral analysis to determine characteristics of the fruit.

[0007] Past proposals involve use of tungsten halogen light sources asstrong emitters of NIR or NIR emitting diode lasers, at wavelengthschosen relative to the band assignments of the character of interest.For example, U.S. Pat. No. 5,708,271 employs NIR lasers directed at thecenter of the fruit at an angle of other than 0° and 180°, and commonly40° to 60°, to the line of the detector and fruit center.

SUMMARY OF THE INVENTION

[0008] In essence the subject invention has means to pass fruit past asensor head positioned adjacent a near infra-red light source, thesensor head being coupled to a spectrometer via fibre opticscharacterised in that the sensor head is positioned substantiallyparallel with the light from the light source, the fibre optics sensingonly the internally reflected or refracted light emanating from thefruit.

DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the present invention will now be described by wayof example only with reference to their accompanying drawings in which:

[0010]FIG. 1 is a schematic illustration of one embodiment of an opticalsensing unit;

[0011]FIG. 2 is a schematic illustration of another embodiment of anoptical light sensing unit;

[0012]FIG. 3 is a cross sectional view of a sensing unit in accordancewith a third embodiment; and

[0013]FIG. 4 is a plan view of the unit of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0014] The FIGS. 1 and 2 show two schematic illustrations of opticalsensing units that are used to spectrally assess the characteristics ofmelons. The melons are placed on a cup that forms part of a conveyor.The sensing unit 10 is mounted on a support structure (not shown) to bein close proximity to the periphery of the melons as they pass theoptical unit. The optical unit has an incandescent light source 11,namely tungsten halogen, positioned centrally of a parabolic reflector12. The mouth 13 of the reflector 12 is provided with an annularaperture 15 with a circular opening and the geometry of the reflector 12is designed so that light leaves the reflector 12 as a collimated beamto effectively impinge radially on the fruit. A probe in the form of acylinder 20 having a closed end 21 and an open mouth 22 is positionedwith the mouth 22 of the cylinder 20 approximately 20 to 30 millimetresfrom the periphery of the melon.

[0015] The probe is coated in a suitable matt black non light-reflectivecoating and includes a cylindrical chamber 23 in which is mounted areflective mirror 25 at one end extending at 45 degrees to the axis ofthe cylinder 20. The wall of the cylinder is provided with a smallaperture 26 into which are housed the fibre ends 30 of a fibre opticcable (not shown) that extends back to a spectrometer (not shown). Themouth 22 of the probe has a stepped recess 32 which houses a plain glasswindow 35. The probe has the effect of blocking some of the parallelbeams of light from the parabolic reflector 12 thus leaving a shadow onthe surface of the fruit beneath the probe. The light outside the shadowhits the fruit as a collimated beam and then as it enters the fruit itbecomes refracted and reflected by the interior of the fruit. Thereflected and refracted light from the shaded area can be picked up by ahighly sensitive sensor after reflecting off the surface of the internalmirror 15 and being transmitted to be picked up by the fibre opticcable.

[0016] A similar optical unit is shown in FIG. 2 except that in thatembodiment the plain glass window 35 has been replaced by a convex lens43 that has the effect of making the radius of the viewed areaindependent of the distance from probe to fruit surface. In all otheraspects this unit is the same as the unit shown in FIG. 1.

[0017] The signal picked up by the optical unit can be passed to aspectrometer which can then carry out the analysis necessary todetermine various parameters of the fruit especially the sweetness ofthe fruit.

[0018] An important advantage that flows from this development is thecapacity to speedily view all fruit in a batch by passing each piece offruit past the optical unit. For some years it has been known to providefruit handling equipment whereby fruit of various types is positionedindividually on a carrying cup attached to a chain conveyor. The fruitcan be rotated past a photographic zone that would contain a CCD camera.The camera would be able to note the size, colour and blemishes on thefruit. This information would be fed to a computer which thenorchestrates ejection means to cause the fruit to be ejected from theconveyor into bins categorised by size, weight or colour. When equipmentof this kind is used with the optical sensing units described above itwill be understood that the optical sensing units will be mounted onmeans that incorporates some form of servo motor control that allows theposition of the head relative to the fruit to vary in dependence of thesize of the fruit. It has been discovered that 20 millimetres is theoptimum distance from the lens of the unit to the periphery of the fruitand to ensure that the unit remains at this optimum distance thecomputer will note the size of the fruit and then instruct the servomotor to move the head to ensure there is always a gap of approximately20 millimetres.

[0019] It is however understood that there are other ways ofaccommodating variations in fruit sizes that would not require thesophistication of computerised controlled movement of the optical head.

[0020] The similar optical unit shown in FIG. 2 has the advantage thatthe fruit to sensor distance is less critical. Provided the fruit sizedoes not vary by more that approximately 40 millimetres then this sensorcould be mounted in a fixed position.

[0021] In a third embodiment illustrated in FIGS. 3 and 4, theincandescent light source 11 and parabolic reflector 12 are replaced bythree lasers 51, 52 and 53 that are positioned about an arc on the righthand side of the cylinder 20 of the sensing unit 50 as shown in FIG. 4.The lasers 51, 52 and 53 are each configured to emanate a laser beam atwavelengths of 910 nm, 860 nm and 758 nm respectively. It is howeverunderstood that the NIR wavelengths can vary between 700 and 2500 nm.

[0022] As shown in FIG. 3, the optical sensing unit 50 includes thecylinder 20 with a closed end 21 and an open mouth 22. As in the earlierembodiments, the cylinder is coated in a suitable black non-lightreflective coating and includes a cylindrical chamber 23 in which ismounted a reflective mirror 25 at one end extending at approximately 45°to the axis of the cylinder. As in the second embodiment, a lens 54 ispositioned across the mouth of the open end of the cylinder. The fibreends 30 of the optical fibre cable (not shown) are fed to the unitthrough a suitable coupling 58 that is screwed into the side of thecylinder. The fibre optic cable goes back to a spectrometer (not shown).

[0023] As shown in FIG. 3, the laser beams coming from the three lasers51, 52 and 53 are directed against the sensing unit to cast a shadow onthe surface of the fruit beneath the probe. Some of the laser beamsdirectly contact the fruit and, although not shown in the drawings, itis understood that means such as fibre optics can be provided to controlthe direction of the light emanating from the lasers as collimated lightdirected to the fruit parallel to the sensor. The light that contactsthe fruit is refracted and reflected by the contents of the fruit in thesame manner as the first embodiment and is then picked up via the mirrorand reflected back to the spectrometer through the optical fibre cables.The mirror 25 is mounted on pivot bolt 60 which allows a small degree ofadjustment to the mirror to alter its inclination to the axis of thecylinder. A second bolt 61 then locks the mirror in the selectedposition. The convex lens 54 assists in collecting the reflected signalfrom the surface of the fruit and directing that signal to the desiredposition on the mirror 65.

[0024] This embodiment has the advantage that the sensor can be furtherfrom the surface of the fruit and it is envisaged that the gap can be upto 50 mm. This is particularly useful when the sensor is used in a highspeed assembly with fruit of differing sizes. It is understood that thenumber of lasers can vary and is it is envisaged that more than threecould be provided in an arc around the upper edge of the sensor. Thelasers are comparatively small measuring only 9 mm in diameter. Thelasers could be positioned away from the sensor with fibre opticsterminating at the head. It is further understood that the wavelengthsemanating from the lasers would vary in dependence of the fruitcharacter that is being spectrally assessed.

[0025] The method and apparatus described above has particular use as ameans for measuring in a non-destructive manner the sugar content offruit. For further disclosure of this measuring technique reference ismade to the following patent literature: U.S. Pat. Nos. 5,708,271,5,524,945 and 5,089,701.

1. Apparatus for the spectral assessment of fruit comprising a sensorhead positioned adjacent a near infrared light source, the sensor headbeing coupled to a spectrometer via fibre optics, the sensor head beingarranged to be positioned close to the periphery of fruit, characterisedin that the sensor head is positioned substantially parallel with thelight from the light source whereby the fibre optics sense only theinternally reflected or refracted light emanating from the fruit. 2.Apparatus according to claim 1 wherein the light source comprises anincandescent light source positioned in front of a parabolic reflectorso that in use the exeunt light is in a collimated beam and the sensorhead casts a shadow on the fruit.
 3. The apparatus according to claim 1wherein the light source comprises a plurality of lasers eitherpositioned close to the sensor head or coupled to fibre opticsterminating close to the sensor head.
 4. The apparatus according toclaim 3 wherein the lasers are collimated optics to direct beamsparallel to the sensor head.
 5. The apparatus according to claim 3wherein the lasers are positioned so that the beams of the lasersreflect off the sensor head to form a shadow on the fruit.
 6. Theapparatus according to any one of claims 3 to 5 wherein the beamemanating from each laser is of a different wavelength.
 7. The apparatusaccording to claim 6 wherein the wavelengths of the laser beams varybetween 700 and 2500 nm.
 8. The apparatus according to claim 7 whereinthree lasers are used, the wavelengths of the light beams beingrespectively 910 nm, 860 nm and 758 nm.
 9. The apparatus according toany one of the preceding claims wherein the sensor head is in the formof a small open ended cylinder, the open end of the cylinder beampositioned in close proximity to the periphery of the fruit, thecylinder containing a mirror so that light emanating from the shadow onthe fruit is reflected by the mirror to be transferred by the fibreoptics to an associated spectrometer.
 10. The apparatus according toclaim 9 wherein a suitably configured lens is positioned across the openend of the cylinder.
 11. Apparatus according to any one of the precedingclaims comprising conveying means to support fruit to pass the sensorhead in close proximity to the head.
 12. The apparatus according toclaim 11 wherein the spacings between the periphery of the fruit and theopen end of the cylinder is between 20 and 50 mm.
 13. A method of aspectral assessment of fruit comprising passing the fruit past a sensorhead positioned adjacent a near infrared light source, the sensor headbeing coupled to a spectrometer via fibre optics characterised by thesteps of positioning the sensor head substantially parallel with thelight from the light source, transferring only the internally reflectedor refracted light emanating from the fruit to the spectrometer via thefibre optics and conducting a spectral analysis of the light.
 14. Themethod of claim 13 comprising placing the fruit on a conveyor andmounting the sensor head in close proximity above the periphery of thefruit.
 15. The method of either claim 13 or 14 comprising positioningthe sensor head in front of the light source to cast a shadow on thefruit and conducting spectral analysis on the light emitted from theshadow.